Some internal combustion engines recirculate exhaust gas from an engine exhaust system to an engine intake system, a process referred to as exhaust gas recirculation (EGR), to reduce regulated emissions, among other purposes. For example, an internal combustion engine may include an EGR system which recirculates exhaust gas from an exhaust passage to an intake passage (e.g., intake manifold). Recirculated exhaust gas may be combined with fresh intake air drawn into the intake passage resulting in a mixture of fresh intake air and recirculated exhaust gas. An EGR valve may be controlled to adjust the amount of recirculated exhaust gas flow and achieve a desired intake air dilution based on engine operating conditions. More specifically, the exhaust gas routed through the EGR system may be measured and adjusted based on various engine operating conditions (e.g., engine speed, load, etc.) during engine operation to maintain desirable combustion stability of the engine while providing emissions and fuel economy benefits. The EGR system may be operated for other purposes as well, for example to increase heat flux to aftertreatment devices during an engine and catalyst warm-up phase.
Further, some internal combustion engines include devices such as throttle turbine generator to collect energy from a pressure difference across an intake throttle that may otherwise be wasted. In some examples, a turbine may be positioned in an intake passage and mechanically coupled to a generator which may generate and supply current to a battery of the engine. By charging the battery in this way, fuel economy of the engine may be improved, as compared to charging the battery with an engine driven generator.
EGR systems (e.g., due to an EGR cooler) can generate condensation in an engine intake system. Such condensation can adversely affect fuel combustion in the engine.
U.S. Pat. No. 8,205,602 discloses an internal combustion engine that utilizes EGR. To mitigate condensation produced by an EGR cooler and introduced into an intake system of the engine, a condensation collection system is utilized. Specifically, a condensation line includes an inlet coupled to the intake system and an outlet coupled to a condensation accumulator. A condensation expulsion line is coupled to an output port of the condensation accumulator. A portion of the condensation expulsion line is disposed in contact with an engine exhaust pipe so that, depending on operation of a condensation control valve disposed within the intake system, condensation in the intake system may be expelled therefrom.
The inventors herein have recognized that throttle turbines can also cause the generation of condensation in an engine intake system.
U.S. Pat. No. 8,763,385 discloses an engine system including a throttle turbine generator including a turbine that drives an auxiliary generator. A throttle bypass valve may be controlled to adjust airflow through a throttle bypass in which the turbine is placed, in turn controlling the extent to which the auxiliary generator is driven. The throttle bypass valve may be controlled according to various operating conditions, including airflow to the engine and a state of charge of an engine battery.
The inventors herein have recognized issues with both approaches. In the first approach, inclusion of a condensation collection system introduces additional cost, complexity, and packaging space to the internal combustion engine. In the second approach, the throttle bypass valve is controlled without regard to the potential of the formation of condensation in the intake system. In some examples, the outlet temperature of gasses flowing out of the turbine may decrease linearly with turbine efficiency. This may also lead to condensation in the intake system, which can adversely affect fuel combustion as described above, and/or icing near the throttle body, which can potentially degrade throttle operation.
One approach that at least partially addresses the above issues includes a method of operating a throttle bypass turbine comprising controlling a temperature of outlet gas flowing out of the turbine by routing the outlet gas through an exhaust gas recirculation heat exchanger positioned in an exhaust gas recirculation passage, the turbine coupled to an intake passage.
In a more specific example, the temperature of the outlet gas is controlled according to one or both of a dew point and an icing point at which condensation and icing respectively form in the intake passage.
In another aspect of the example, the temperature of the outlet gas is controlled by adjusting a flow rate of exhaust gas through the exhaust gas recirculation passage.
In yet another aspect of the example, a temperature of a mixture of the outlet gas and intake air in the intake passage is controlled by adjusting a flow rate of the outlet gas
In this way, condensation and/or icing in an intake passage, at least partially caused by cooling across a throttle bypass turbine, may be reduced or prevented. Thus, the technical result is achieved by these actions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.